This randomized study is designed to determine whether endurance exercise-training can lower blood pressure (BP) and induce regression of left ventricular hypertrophy (LVH) in older hypertensive men and women. The specific aims are: (1) to determine whether endurance exercise-training can reduce BP; (2) to elucidate mechanisms underlying reduction of BP by evaluation of cardiac output, total peripheral resistance, arterial stiffness, sympathetic nervous system activity, and blood volume; (3) to determine whether exercise-training can (a) induce regression or reduction of LVH, (b) improve left ventricular function, and (c) reduce arterial stiffness; and (4) to determine whether the training-induced decrease in BP is associated with reduction of hyperinsulinemia and intra-abdominal fat. Plans are to recruit 108 older (60-70 yrs of age) men and women with mild-to-moderate hypertension (BP 141/90-170/109 mmHg). The subjects will be randomized into 2 groups: (a) an exercise group that will exercise for 9 mo, and (b) a sedentary control group will be treated with a diuretic (chlorthalidone) and followed for 9-mo. The following procedures will be performed before and after the study: (1) resting BP and 24-hr BP monitoring; (2) cardiac output at rest and during treadmill exercise with the use of acetylene rebreathing method; (3) assessment of arterial stiffness with the use of pulse wave velocity method; (4) venous plasma norepinephrine (NE) concentration at rest and during exercise; (5) steady-state NE kinetics with the isotope dilution method; (6) blood volume determination; (7) 2-D echocardiogram and Doppler studies at rest and during phenylephrine infusion to evaluate left ventricular function; and (8) diet evaluation, oral glucose tolerance, plasma insulin concentration, and body composition (hydrostatic weighing, and MRI). Exercise-training consists of 1 mo of flexibility exercises and 8 mo of endurance exercise at the intensity 60-70% of maximal 02 uptake (VO2max). The investigators will also enroll 20 healthy men and women of similar age who will exercise to compare differences in cardiovascular adaptations between hypertensive and normotensive subjects.